A secondary battery, which is easily applied to various product groups and has electrical characteristics such as high energy density, is universally applied not only for a portable device but also for an electric vehicle (EV) or a hybrid electric vehicles (HEV), an energy storage system or the like, which is driven by an electric driving source. The secondary battery is attracting attention as a new environment-friendly energy source for improving energy efficiency since it gives a primary advantage of reducing the use of fossil fuels and also does not generate by-products by the use of energy at all.
Secondary batteries widely used at the preset include lithium ion batteries, lithium polymer batteries, nickel cadmium batteries, nickel hydrogen batteries, nickel zinc batteries and the like. An operating voltage of the unit secondary battery cell, namely a unit battery cell, is about 2.5V to 4.2V. Therefore, if a higher output voltage is required, a plurality of battery cells may be connected in series to configure a battery pack. In addition, depending on the charge/discharge capacity required for the battery pack, a plurality of battery cells may be connected in parallel to configure a battery pack. Thus, the number of battery cells included in the battery pack may be variously set according to the required output voltage or the demanded charge/discharge capacity.
Meanwhile, when a plurality of battery cells are connected in series or in parallel to configure a battery pack, it is common to configure a battery module composed of a plurality of battery cells first, and then configure a battery pack by using a plurality of battery modules and adding other components.
A battery pack of a multi-battery module structure is manufactured so that a plurality of secondary batteries are densely packed in a narrow space, and thus it is important to easily discharge the heat generated from each secondary battery. The secondary battery is charged or discharged by means of electrochemical reactions as described above. Thus, if the heat of the battery module generated during the charging and discharging process is not effectively removed, heat accumulation occurs, which may promote the deterioration of the battery module and in occasions may cause ignition or explosion.
Therefore, a high-output large-capacity battery pack requires a cooling device that cools battery cells included therein.
Generally, the cooling device is classified into two types of cooling device, namely an air cooling type and a water cooling type, but the air cooling type is more widely used than the water cooling type due to short circuit or waterproofing of the secondary battery.
Since one battery cell may not produce a large power, a commercially available battery module generally includes a plurality of battery cells as many as necessary so as to be stacked and packaged in a module case, and a battery pack includes a plurality of battery modules as many as necessary so as to be stacked and packaged therein. In addition, in order to keep the temperature of the secondary battery at a proper level by cooling the heat generated while each battery cell is producing electricity, a plurality of cooling pins corresponding to the area of the battery cells are inserted as a heat dissipating member throughout the battery cells. The cooling pins absorbing heat from each battery cell are connected through a cooling plate to a heat sink provided at a bottom of the battery pack and transfer the heat thereto. The heat sink is cooled by cooling water or cooling air.
In addition, in a conventional battery pack, due to the plurality of cooling pins, the cooling plate and the heat sink interposed between the battery cells, the energy density of the battery cells is lowered as much as these components, and the manufacture cost is increased due to these components.